1. Field of Invention
This invention relates to a method and a system for high-resolution retinal imaging, eye aberration compensation, and diagnostics based on adaptive optics with direct optimization of an image quality metric using a stochastic parallel perturbative gradient descent technique.
Adaptive optics is a promising technique for both diagnostics of optical aberrations of the eye and substantially aberration-free high-resolution imaging of the retina. In existing adaptive optics techniques adaptive correction is based on illumination of the retina by a collimated laser beam to create a small size laser location on the retina surface with consequent measurement of phase aberrations of the wave scattered by the retina tissue. Correction of eye optical aberrations is then performed using the conventional phase conjugation technique.
This traditional approach has several important drawbacks. One important drawback is the danger due to an invasive use of the laser beam focused onto the retina. Other drawbacks include overall system complexity and the high cost of the necessary adaptive optics elements such as a wavefront sensor and wavefront reconstruction hardware. More importantly, due to aberrations the laser beam location size on the retina is not small enough to use it as a reference point-type light source and hence conjugation of the measured wavefront does not result in optimal optical aberration correction. Additionally, the traditional approach can produce a turbid image that can make performing an operation with a microscope difficult.
One prior art method using a laser is taught in U.S. Pat. No. 6,095,651 entitled “Method and Apparatus for Improving Vision and the Resolution of Retinal Images”, issued to Williams, et al. on Aug. 1, 2000. In Williams, et al. teaches a method and apparatus for improving resolution of retinal images. In this method, a point source of light is produced on the retina by a laser beam. The source is reflected from the retina and received at a lenslet array of a Hartman-Shack wavefront sensor. Thus, higher order aberrations of the eye can be measured and data can be obtained for compensating the aberrations using a system including a laser. U.S. Pat. Nos. 5,777,719 and 5,949,521 provide essentially the same teachings. While these references teach satisfactory methods for compensating aberrations, there is some small risk of damaging the retina since these methods require applying laser beams to the retina.
U.S. Pat. No. 5,912,731, entitled “Hartmann-type Optical Wavefront Sensor” issued to DeLong, et al. on Jun. 5, 1999 teaches an adaptive optics system using adjustable optical elements to compensate for aberrations in an optical beam. The aberrations may be caused, for example, by propagation of the beam through the atmosphere. The aberrated beam can be reflected from a deformable mirror having many small elements, each having an associated separate actuator.
Part of the reflected beam taught by DeLong can be split off and directed to impinge on a sensor array which provides measurements indicative of the wavefront distortion in the reflected beam. The wavefront distortion measurements can then be fed back to the deformable mirror to provide continuous corrections by appropriately moving the mirror elements. Configurations such as this, wherein the array of small lenses as referred to as a lenslet array, can be referred to as Shack-Hartmann wavefront sensors.
Additionally, DeLong teaches a wavefront sensor for use in measuring local phase tilt in two dimensions over an optical beam cross section, using only one lenslet arrangement and one camera sensor array. The measurements of DeLong are made with respect to first and second orthogonal sets of grid lines intersecting at points of interest corresponding to positions of optical device actuators. While this method does teach the way to correct aberrations in a non-laser light system, it cannot be used in cases where lasers are required.
U.S. Pat. No. 6,007,204 issued to Fahrenkrug, et al. entitled “Compact Ocular Measuring System”, issued on Dec. 28, 1999, teaches a method for determining refractive aberrations of the eye. In the system taught by Fahrenkrug, et al. a beam of light is focused at the back of the eye of the patient so that a return light path from the eye impinges upon a sensor having a light detecting surface. A micro optics array is disposed between the sensor and the eye along the light path. The lenslets of the micro optics array focus incremental portions of the outgoing wavefront onto the light detecting surface so that the deviations and the positions of the focused portions can be measured. A pair of conjugate lenses having differing focal lengths is also disposed along the light path between the eye and the micro optics array.
U.S. Pat. No. 6,019,472, issued to Koester, et al. entitled “Contact Lens Element For Examination or Treatment of Ocular Tissues” issued on Feb. 1, 2000 teaches a multi-layered contact lens element including a plurality of lens elements wherein a first lens element has a recess capable of holding a volume of liquid against a cornea of the eye. A microscope is connected to the contact lens element to assist in the examination or treatment of ocular tissues.
U.S. Pat. No. 6,086,204, issued to Magnante entitled “Methods and Devices To Design and Fabricate Surfaces on Contact Lenses and On Corneal Tissue That Correct the Eyes Optical Aberrations” on Jul. 11, 2000. Magnante teaches a method for measuring the optical aberrations of an eye either with or without a contact lens in place on the cornea. A mathematical analysis is performed on the optical aberrations of the eye to design a modified shape for the original contact lens or cornea that will correct the optical aberrations. An aberration correcting surface is fabricated on the contact lense by a process that includes laser ablation and thermal molding. The source of light can be coherent or incoherent.
U.S. Pat. No. 6,143,011, issued to Hood, et al. entitled “Hydrokeratome For Refractive Surgery” issued on Nov. 7, 2000 teaches a high speed liquid jet for forming an ophthalmic incisions. The Hood, et al. system is adapted for high precision positioning of the jet carrier. An airway beam may be provided by a collimated LED or laser diode. The laser beam can be used to align the system.
U.S. Pat. No. 6,155,684, issued to Billie, et al. entitled “Method and Apparatus for Precompensating The Refractive Properties of the Human Eye With Adaptive Optical Feedback Control” issued on Dec. 5, 2000. Billie, et al. teaches a system for directing a beam of light through the eye and reflecting the light from the retina. A lenslet array is used to obtain a digitized acuity map from the reflected light for generating a signal that programs an active mirror. In accordance with the signal the optical paths of individuals beams in and the beam of light are made to appear to be substantially equal to each other. Thus, the incoming beam can be precompensated to allow for the refractive aberrations of the eyes that are evidenced by the acuity map.
Additional methods for using adaptive optics to compensate for aberrations of the human eye are taught in J. Liang, D. Williams and D. Miller, “Supernormal Vision and High-Resolution Retinal Imaging Through Adaptive Optics,” J. Opt. Soc. Am. A, Vol. 14, No. 11, pp. 2884–2891, 1997 and F. Vargas-Martin, P. Prieto, and P. Artal, “Correction of the Aberrations in the Human Eye with a Liquid-Crystal Spatial Light Modulator: Limits to Performance,” J. Opt. Soc. Am. A, Vol. 15, No. 9, pp.2552–2561, 1998. Additionally, J. Liang, B. Grimm, S. Goelz, and J. Bille, “Objective Measurement of Wave Aberrations of the Human Eye with the Use of a Hartmann-Shack Wave-Front Sensor,” J. Opt. Soc. Am. A, Vol. 11, No. 7, pp. 1949–1957, 1994 teaches such a use of adaptive optics.
Furthermore, it is known in the art to use a PSPGD optimization algorithm in different applications. For example, see M. Vorontsov, and V. Sivokon, “Stochastic Parallel-Gradient-Descent Technique for High-Resolution Wave-Front Phase-Distortion Correction,” J. Opt. Soc. Am. A, Vol. 15, No. 10, pp. 2745–2758, 1998. Also see M. Vorontsov, G. Carhart, and J. Ricklin, “Adaptive Phase-Distortion Correction Based on Parallel Gradient-Descent Optimization,” Optics Letters, Vol. 22, No. 12, pp. 907–909, 1997.
It is well known in the art to scan an iris and obtain an iris biometric image. See, for example, U.S. Pat. Nos. 4,641,349, 5,291,560, 5,359,669, 5,719,950, 6,289,113, 6,377,699, 6,526,160, 6,532,298, 6,539,100, 6,542,624, 6,546,121, 6,549,118, 6,556,699, 6,594,377, 6,614,919, and U.S. Patent Application Nos. 20010026632A1, 20020080256A1, 20030095689A1, 20030120934A1, 20020057438A1, 20020132663A1, 20030018522A1, 20020158750A1. However, such images were often not optimal and their applicability was somewhat limited.
2. Description of Related Art
All references cited herein are incorporated herein by reference in their entireties.